Photochromism and electrochromism in pyridinium-annelated perylene diimide salts via charge-assisted anion-π interactions

Organic chromic materials with photochromic and electrochromic properties are promising materials for photoelectric applications. Despite some reports indicating the presence of these properties in aromatic imide derivatives, the advancement of their enduring discoloration performance remains an unresolved challenge. Herein, we incorporated of charge-assisted anion-π interactions into aromatic imide derivatives as a strategy for improving the stability of generated free-radical, and a series of pyridinium-annelated perylene diimides salts (PAPDI-X, X = I−, Br−, Cl−, NO3−, PF6−) were synthesized. With variations in the electron-donating capabilities (Lewis basicity) of the anions, the nature of anion-PDI interactions undergoes a transition from non-chromogenic anion-π interaction to chromogenic anion-induced electron transfer (ET) phenomenon, and these interactions have been fully characterized by UV/Vis, NMR, and EPR spectroscopies. Among the evaluated anions, Br- anion with moderate Lewis basicity participates in ET with PAPDI by light or voltage stimuli, and generate stable PAPDI-Br•− radical anion and PAPDI-Br2- dianion in aprotic solvent or in solid state, thus making PAPDI-Br exhibit distinctive photo/electrochromic dual responsive behavior based on radical formation. This meaningful design provides new concepts for the design of organic chromic materials and shows great prospects in optoelectrical materials.